 /*
 * jQuery.appear
 * https://github.com/bas2k/jquery.appear/
 * http://code.google.com/p/jquery-appear/
 *
 * Copyright (c) 2009 Michael Hixson
 * Copyright (c) 2012 Alexander Brovikov
 * Licensed under the MIT license (http://www.opensource.org/licenses/mit-license.php)
 */
(function($) {
	$.fn.appear = function(fn, options) {

		var settings = $.extend({

			//arbitrary data to pass to fn
			data: undefined,

			//call fn only on the first appear?
			one: true,

			// X & Y accuracy
			accX: 0,
			accY: 0

		}, options);

		return this.each(function() {

			var t = $(this);

			//whether the element is currently visible
			t.appeared = false;

			if (!fn) {

				//trigger the custom event
				t.trigger('appear', settings.data);
				return;
			}

			var w = $(window);

			//fires the appear event when appropriate
			var check = function() {

				//is the element hidden?
				if (!t.is(':visible')) {

					//it became hidden
					t.appeared = false;
					return;
				}

				//is the element inside the visible window?
				var a = w.scrollLeft();
				var b = w.scrollTop();
				var o = t.offset();
				var x = o.left;
				var y = o.top;

				var ax = settings.accX;
				var ay = settings.accY;
				var th = t.height();
				var wh = w.height();
				var tw = t.width();
				var ww = w.width();

				if (y + th + ay >= b &&
					y <= b + wh + ay &&
					x + tw + ax >= a &&
					x <= a + ww + ax) {

					//trigger the custom event
					if (!t.appeared) t.trigger('appear', settings.data);

				} else {

					//it scrolled out of view
					t.appeared = false;
				}
			};

			//create a modified fn with some additional logic
			var modifiedFn = function() {

				//mark the element as visible
				t.appeared = true;

				//is this supposed to happen only once?
				if (settings.one) {

					//remove the check
					w.unbind('scroll', check);
					var i = $.inArray(check, $.fn.appear.checks);
					if (i >= 0) $.fn.appear.checks.splice(i, 1);
				}

				//trigger the original fn
				fn.apply(this, arguments);
			};

			//bind the modified fn to the element
			if (settings.one) t.one('appear', settings.data, modifiedFn);
			else t.bind('appear', settings.data, modifiedFn);

			//check whenever the window scrolls
			w.scroll(check);

			//check whenever the dom changes
			$.fn.appear.checks.push(check);

			//check now
			(check)();
		});
	};

	//keep a queue of appearance checks
	$.extend($.fn.appear, {

		checks: [],
		timeout: null,

		//process the queue
		checkAll: function() {
			var length = $.fn.appear.checks.length;
			if (length > 0) while (length--) ($.fn.appear.checks[length])();
		},

		//check the queue asynchronously
		run: function() {
			if ($.fn.appear.timeout) clearTimeout($.fn.appear.timeout);
			$.fn.appear.timeout = setTimeout($.fn.appear.checkAll, 20);
		}
	});

	//run checks when these methods are called
	$.each(['append', 'prepend', 'after', 'before', 'attr',
		'removeAttr', 'addClass', 'removeClass', 'toggleClass',
		'remove', 'css', 'show', 'hide'], function(i, n) {
		var old = $.fn[n];
		if (old) {
			$.fn[n] = function() {
				var r = old.apply(this, arguments);
				$.fn.appear.run();
				return r;
			}
		}
	});

})(jQuery);